Endoplasmic Reticulum

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Endoplasmic Reticulum
2015-11-26 08:06:27

Endoplasmic Reticulum
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  1. What mechanism translates the mRNA
  2. What is the role of tRNA
    tRNA carries the amino acid to the ribosome to be assembled into a polypeptide bond
  3. How many amino acids make up a protein
    No more then 20
  4. Once the polypeptide bond exits the ribosome, what does it do next
    It folds to protect the hydrophobic sections, chaperones assist by protecting these until folded
  5. What is the difference between co-translational protein targeting and post-translational protein targeting
    • Co- Delivers to the membrane while translating
    • Post- Delivers to the membrane after translating
  6. What are some examples of Chaperones
    • hsp70 family (cytosol) BiP (ER)
    • GroEL family
  7. How many ER are in each Cell
    Only one
  8. What is the ER
    Membrane bound compartment in the cytoplasm of Eukaryotic cells where lipids are sythesized and membrane bound proteins and secretory proteins are made
  9. How are the ER tubules held in place
    By microtubules
  10. Is there seperation between rough and smooth ER
    No, they are continuous
  11. What are the primary functions of the smooth ER
    • Lipid biosythesis (cholesterol, phospholipids, ect)
    • Detoxification
  12. What are the important enzymes in the smooth ER for detoxyfication
    Cytochrome p450s
  13. Where are the new phospholipids inserted when produced
    Into the leaflet of bilayer facing the cytosol
  14. What is a scramblase
    A membrane bound phospholipid translocator, used to transfer phospholipids one side to the other, bidirectionally (Only works in the ER)
  15. Where is Flippase used, and for what purpose
    In the plasma membrane to flip phosphatidylserine and phosphatidylethanolamine from the cells exterior to its interior creating an asymmetric bilayer
  16. How is phosphatidylserine different from the other phopholipids
    It is negatively charged and is placed only on the cytosol side, creating a negative charge on the cytosol side when there are no other molecules present
  17. How is floppase different from flippase
    Floppase moves the phospholipids from the cytosol side to the extracellular side
  18. If a cell required more cholesterol then normal, what would one expect
    More smooth ER since this is where it is made. They can proliferate when needed however
  19. What are the three ways that lipids are transported
    • 1. Through the smooth to the rough ER membrane
    • 2. By vesicles budding off the smooth ER to fuse eith other membranes (vesicular trafficking)
    • 3. By transfer proteins to those organelles that don't accept vesicular traffic from the ER (Mitochondria)
  20. Why would steroid synthesis engage smooth ER synthesis
    Because steroid hormones are synthesized from cholesterol made there
  21. What is vesicular traffic
    When vesicles bud off of ER for movement to other regions of the cell
  22. Another way lipids are delivered is by a random scattering in the cell accompanied by what
    Transfer proteins
  23. Ingested alcohol is broken down it what different sites
    Peroxisomes and Smooth ER
  24. What is the drug phenobarbitral used for, and how is it broken down
    It is a widely used anti-convulsant, and is broken down in the smooth ER.
  25. How fast can the ER double in size
    In a few days
  26. What cation is found in very high rates in the ER
    Ca++ used for cellular signals
  27. Secretory and membrane proteins are targeted during synthesis to the rough ER by
    ER signal sequence or peptide
  28. What is an SRP (signal recognition protein)
    It pauses the co-translation and delivers it to the ER membrane to finish translation, then it leaves
  29. Nascent (Just born) protein is a protein signal sequence and directs ribosomes to
  30. What is a co translation transport
    Transportation while the protein is being translated. The transportation is to the ER membrane
  31. What is the role of the signal peptidase
    It stops the co-translational coding when signaled by the stop sequence making a membrane bound protein
  32. In what ways can a protein that enters the ER be modified
    • 1. The N- terminal is often cleaved by a signal peptidase leaving it in the membrane
    • 2. Most of the proteins that end up in the ER lumen receive N linked glycosylation aiding in folding
    • 3. Formation of disulfide bonds which aides in folding
    • 4. Some lose transmembrane domain and gain a GPI anchor
    • 5. Protein folds
  33. How do proteins get to be a membrane bound protein
    They are threaded in like a sewing machine by a translocation channel then stopped by signal peptidase
  34. Multi subunit complexes like antibodies are held together by what, assembled in the ER
    Disulfide bonds
  35. What is a GPI anchor
    It helps in directing membrane bound proteins to special places in the plasma membrane like the caveolae
  36. Disulphide bonds of complexes of membrane proteins like an antibody are assembled where
  37. Normal new proteins are transferred from the ER to the
  38. What happens to a protein if it is not folded properly
    It is sent to the cytosol and degraded
  39. Why is correct folding of porteins necessary
    They can't leave the ER unless they are folded properly and released from chaperones
  40. What is a disease relating to the incorrect folding of a protein in the ER
    Cystic Fibrosis
  41. Cystic Fibrosis is caused by mutations in the CFTCR (Cystic fibrosis transmembrane conductance regulator) which
    Codes for a protein that transports chloride ions in and out of epithelial cells. Therefore the cells fill with fluid and burst creating a thick discharge. The mutant protein is misfolded and therefore stay in the ER and are degraded
  42. N-Linked Glycosylation is received by many proteins that enter the ER for
    Assistance in correct folding
  43. Why is the rough ER rough, what is happening
    Ribosomes are attached to it synthesizing proteins into the lumen